Aftermarket and Dealer Add Ons

Superchargers and Performance

These pages contain images of period accessories for the MGTD. Select each image to see an enlarged view.

Note: A great site on superchargers for the T-Series can be found at the T-ABCs Forever Gallery.


			Dual Exhaust Manifold

For the racing MG owner, this tubular push-rod and special tappet will considerably lighten the valve train. On more recent models the oil hole has been relocated for better lubrication at all speeds	Engine accessories are a book unto themselves, but here is one that has been quite successful. It is a Lucas magneto kit ,with all necessary parts for installation including a valve side plate with breather openings	Derrington headers for the MGTD.
Laystall-Lucas alloy head	Laystall-Lucas alloy head	Laystall-Lucas alloy head
		Marshall supercharger intake

Supercharger Information

The following contains information on various superchargers that were available for the MGTD during its production period.

Arnott

This text comes from pages 463 thru 465 of the MG WORKSHOP MANUAL and was supplied to this site by Willem Janssen of Holland who has installed this supercharger on his MGTD.

THE ARNOTT LOW PRESSURE INSTALLATION FOR TA, TC AND TD SERIES MIDGET.

The Arnott supercharger, which is manufactured by Carburetors Ltd., Grange Road, London, N.W.10, England, is a vane type pump, having an inbuilt feature which enables pressure to rise within the supercharger before transmitting to the manifold this being attained by the late opening of the outlet port. Not only are pumping losses avoided, but this has strong influence in preventing surge. A further reduction in power required to drive the vane type supercharger is due to progressive reduction of vane area exposed to pressure as compression rises within the supercharger. The Model 1600 supercharger is used in the low pressure installation shown in fig. 7. Kits are supplied with all parts required for the complete conversion and fitting instructions are enclosed to enable any competent amateur mechanic to do the work himself. A special manifold replaces the twin carburetters and the supercharger mounts directly on the centre. The extended drive shaft is directly coupled to the supercharger, requiring no universal joint and subsequently, no servicing. A grease pump connection is provided for the roller race drive pulley bearing.

Fig. 7. Arnott Supercharger installation

In addition to the supercharger pulley, two other pulleys are provided. The triple-V-cast iron crankshaft pulley replaces the standard one providing the twin drive to the supercharger. The light alloy fan pulley replaces the original giving clearance to the two supercharger belts. When fitting the fan pulley care must be taken to see that the ends of the 5 mm bolts securing the fan do not protrude through the flange. The front of the supercharger extended drive which is encased in a light alloy housing, is supported from the front cylinder head stud and by a vertical stay from the front engine plate. The underside of the header tank support will need to be reduced slightly to enable easy belt changes, and the radiator support tube is refitted lower down the side of the radiator using the plate and pacers, etc., supplied.

The Arnott low pressure supercharger has as its primary object the supplying of petrol / air mixtures to the inherent volumetric efficiency associated with the unblown engine.

The capacity of the supercharger together with the speed at witch it is driven are chosen so that approximately 33 1/3% greater volume is available to the engine. This percentage is closely reflected in "before and after" performance figures or differently expressed, the power weight ratio is improved by 33 1/3%. In addition to the improvement in acceleration the benefits of a well atomized and mixed gas is very apparent during part throttle conditions which is reflected in fuel economy. The engine also runs more smoothly given the feel of a six cylinder engine to a four cylinder one.

The reduced atmospheric pressure at high altitudes causes a drop in the efficiency of any normally carbureted engine. This loss can very easily be overcome by the use of a low pressure supercharger. The use of V-belt drive and the freedom from any gearing within the supercharger, combined with well designed ports ensures quietness of operation.

LUBRICATION

In the Arnott supercharger all vane and shaft journals run on ball races, and all races and components are lubricated via the hollow van shaft to which is fed oil from a separate quart size oil tank. Oil passes to the supercharger through a calibrated orifice situated in the tank, being air bled from within the tank it ensures the free delivery, of oil, through the pipe lines and also to prevent any syphoning action. This calibrated orifice requires no attention as it is protected by gauze of much finer mesh than would permit a blockage. A pressure balance pipe conveys the manifold pressure to the interior of the oil tank, the oil supply to the supercharger being based upon the fact that there is always less pressure within the rotor than in the manifold. This is so whether the throttle is closed or open, and therefore the inside of the tank is variably pressurized at all times in accordance with the conditions prevailing. The oil feed pipes are internally armored P.V.C. tubing, this providing flexibility between supercharger and tank. These should never be replaced by larger bore or rubber lined pipes, or the even delivery of the oil will be impaired.

MAINTENANCE

The servicing of the supercharger installation is limited to three points.

The oil supply requires replenishing every 800/900 miles.
The replacement of drive belts after long periods
Applications of a grease gun to the front bearing greaset when normal car servicing is being carried out.

It will be appreciated that the passage of oil through the supercharger, using the Arnott system described above, ensures a constant supply of upper cylinder lubricant giving a long life to the cylinder bores.

CARBURETION

The front one of the original S.U. carburetters can be used with the standard Arnott installation. The jet control lever is moved to the outside and a special control, on the TD Midget set, is fitted to enable the opening of the throttle when starting. The standard throttle control link can be used with the extension clamp link provided. A double ended union connects the petrol pipes. The float chamber of this carburetter faces the outside. Performance at the "top-end" can be increased by the fitting of the 1 1/2" in. diameter S.U. carburetter, for which a special elbow can be supplied. As further alternatives special Arnott carburetters are available, these being fitted directly to the inlet port of the supercharger, eliminating the use of an elbow and ensuring freedom from vaporization, difficult cold starting and giving improved performance throughout the range. Two sizes are available, the 1 1/4 in. diameter normally supplied and the 1 1/2" in. diameter used for competitions and improved "top-end".

AIR CLEANER

Unless the atmosphere is very dry and dusty, it is preferable to remove the air cleaner, as the capacity is insufficient for the efficient breathing of the engine at high revolutions. When the climate demands however it should be fitted and it is possible to enlarge the effective area of the filter.

IGNITION

With a supercharger engine there is a distinct advantage in locking the automatic advance and retard mechanism fitted to the distributor. Removal of the distributor cover and the contact breaker plate, will expose the centrifugally operated weights, witch are controlled by two springs hooked into a hole in each weight. There are usually additional holes into which the springs should be hooked. Where there are slots instead of holes, a small tag should be soldered across the weights to stop them moving. After replacing the contact breakers plate, etc,. the ignition should be set to give maximum advance.

COMPETITION USE

Although the Model 1600 can be speeded up to give greater boost, the efficiency at higher revolutions shows a definite tendency to fall away. Model 2800 is therefore specified for competition purposes and boost pressures of between 10 lbs. And 15 lbs. per sq. in. are easily available by simply changing the pulley sizes. The Arnott 1 1/2 in. or the 1 1/2 in. or 1 1/4 in. S.U. carburetters are used, and special jets and needles can be obtained from the respective manufacturers to enable Methanol mixtures to be used.

Marshall-Nordec

The Marshall-Nordec supercharger information supplied by Willem van der Veer. The two images to the right can be selected to see the original scan. The top image has been converted to text on the left.

Supercharger Installation

The Marshall-Nordec Low-Pressure Supercharger Installation has been designed and produced particularly for use on the standard popular car of medium horsepower. It is precision built throughout and embodies all the latest improvements arising from over 20 years development.

The illustration above, shows details of the compressor and drive assembly. All installations incorporate the famous Marshall Rootes type compressor which is available in a complete range of sizes to deal with the requirements of engines from 750cc to 4,000cc. For 1 to 1.5 litre engines, a J75 model is used. This has a nominal displacement of 75 cu. ft. of free air per minute at a speed of 3000 RPM, and when driven at approximately 1.3/1 engine speed produces upto 6 lbs PSI boost pressure.

The compressor is built of light alloy castings and has two twin-lobed rotors which are driven through specially hardened gears. These rotors made of light alloy, are of involute form and are cut directly on to high tensile steel shafts and dynamically balanced after machining. The drive for the compressor is enclosed in a nosepiece casting which is extended forward to a convenient point to accommodate the front drive pulley. Enclosed in the nosepiece is a shaft mounted and running on bearings, and a simple coupling device. On standard installations a single driving belt from crankshaft pulley to supercharger is used.

This precision built unit forms the basis of all Marshall-Nordec installations, also included are the necessary inlet and outlet manifolds, fixing brackets, crankshaft and jockey pulleys, lubrication arrangements etc. These parts are designed for each individual car and can normally be fitted without alteration to the standard engine unit.

The installation will operate satisfactorily with any carburettor of suitable capacity, the original standard carburettor is usually employed with jet modifications. The oiling arrangements to the supercharger are entirely automatic. A tapping from the engine oil pressure pipe is delivered to the supercharger through an adjustable oil sight-feed and the oil after circulating through the gears and bearings returns to the sump via gravity drain pipe.

Installations are supplied in kit form, and include all the parts necessary to install the equipment. A full size drawing with all parts clearly marked is included with detailed fitting instructions, and enables fitting to be undertaken by any reasonably competent mechanic. The only maintenance required is periodic adjustment of the jockey pulley to ensure the correct drive belt tension, and inspection of the oil adjuster to ensure that oil is supplied to the supercharger. Except for these two points the installation will operate efficiently for long periods without attention.

The popularity of Marshall-Nordec installations is undoubtably due to the simplicity in design of the Marshall 'Rootes' type compressor which provides the highest degree of efficiency with maximum durability, so enabling the supercharger to invariably outlast the life of the engine to which it is fitted. A combination not normally obtained with other types of supercharger.